Process of making a sheet paper

ABSTRACT

A PROCESS OF MAKING A SHEET PAPER IN WHICH AN AQUEOUS DISPERSION CONTAINING SYNTHETIC FIBER, A HOT WATER SOLUBLE FIBER BINDER AND CARBOXYMETHYL CELLULOSE IS PREPARED AND SUBSEQUENTLY, A SHEET PAPER IS FORMED FROM THE AQUEOUS DISPERSION. THE AQUEOUS DISPERSION MAY CONTAIN A FIBROUS MATERIAL HAVING A LOWER MELTING POINT THAN THAT OF THE SYNTHETIC FIBER IN ADDITION TO THE ABOVE INGREDIENTS. A SHEET PAPER FROM THE LATTER AQUEOUS DISPERSION IS SUBJECTED TO HEAT TREATMENT.

July 4, 1972 HARUQ MIYAMOTQ ET AL 3,674,621

PROCESS OF MAKING A SHEET PAPER 2 Sheets-Sheet 1 Filed Feb. 17, 1970INSOLUBLE TROP|C SOLUBLE 0'25 DEGREE OF ETHERIFICATION July 4, 1972Filed Feb. 17, 1970 STRENGTH (BREAKING LENGTH IN km) ARUO MIYAMOTO ETAL3,674,621

PROCESS OF MAKING A SHEET PAPER 2 Sheets-Sheet 2 F/gZ 0 150 c.p.s. I 350.C.p.s. I 75o c.p.s.

DEGREE OF ETHERIFICATION United States Patent 3,674,621 PROCESS OFMAKING A SHEET PAPER Haruo Miyamoto, Hideho Uchida, and Masaru Uehara,

Nagoya, Japan, assignors to Mitsubishi Rayon Company Limited, Tokyo,Japan Filed Feb. 17, 1970, Ser. No. 12,074 Claims priority, applicationJapan, Feb. 25, 1969, 44/ 13,639, 44/ 13,640 Int. Cl. D21f 11/00; D21h5/12 US. Cl. 162-146 24 Claims ABSTRACT OF THE DISCLOSURE The presentinvention relates to a process of making a synthetic fiber paper, moreparticularly, relates to a process of making a synthetic fiber paperlargely or entirely composed of hydrophobic synthetic fiber, forexample, polyolefine fiber, polyester fiber, etc., by using a hot watersoluble fiber binder such as polyvinyl alcohol fiber binder, whichresults in the provision of hydrophobic sheet paper having especiallyexcellent mechanical properties at dry conditions.

Further, the present invention relates to a process of making asynthetic fiber paper which is characterized by a selection of paperstock and conditions of after-treatment, especially heat-treatmentconditions which results in the provision of synthetic fiber paperhaving various prominent appearances or shapes and excellent physicalproperties.

Recently, a development of papers composed of chemical or syntheticfiber, for example, rayon, vinylon, nylon, polyester fiber, etc., hasbeen achieved and many patents and technical papers concerned with theabove have been published. These fibers, however, have manydisadvantages in the production of chemical or synthetic fiber papers aspaper stock for manufacturing, that is, they are not so fibrillatedwithout difficulties, which forms a striking contrast with wood pulp,and they have little or no hydrogen bonding force or bonding force dueto their intertwining properties. Therefore, every effort to create thebonds among fibers and thusly improve tenacity and other mechanicalproperties of the paper has been spent, for example, by improving thesurface property of fibers, by searching for an adequate binder, or byblending a small quantity of synthetic fiber having a lower meltingpoint with the fiber composing a paper as the principal ingredient andheating them to melt or adhere. These methods, however, have both meritsand demerits, and it is indeed difficult to make them fit for practicaluse in the existing paper forming processes.

On the contrary, an appearance of a temperature and humidity sensitivefiber binder, in other words, hot Water soluble fiber binder made from acompound easily soluble in hot water, which was represented by apolyvinyl alcohol fiber binder, has enabled the industrial production ofvinylon paper or rayon paper. Such a fiber binder, in case it is addedat an amount from 5 to 25% 0.W.F. to fibers composing a paper as theprincipal inice gredients, is melted by heat of the dryer (approximatelyC.) and moisture in the wet web on web forming process and forms bondsamong the fibers.

However, in polyolefine or polyester fiber which is hydrophobic initself, even in case such a hot water soluble fiber binder is added tothe principal fiber, so little bonding force may be, contrary toexpectation, practically gained regardless of an amount of the fiberadded, and therefore, it has also been difficult to produce a paperhaving excellent mechanical properties from the above synthetic fiber.

The above difiiculties are thought to arise from the fact that the wetweb on web forming process retains so little water and it has also lessdensity among fibers at a dryer part of the process, additionally theabove hydrophobic fiber has little adhering force to the fiber binder.In the process of forming the web containing hydrophobic fiber as theprincipal ingredient, even though suction and drainage may be reduced,the fiber cannot retain so much water in its inner structure that thewet web just formed contains considerably less water through a dryerpart than that of other chemical or synthetic fibers such as rayon andvinylon, needless to say pulp. Therefore, density of the wet webdecreases and the hot water soluble fiber binder cannot fulfill itsfunction as a binder, so that the sheet has an appearance of so-calledweb in the production of non-woven fabric by a dry process, not beingsimilar to water leaf. That is, even though the wet web containing from10 to 20% by weight of polyvinyl alcohol fiber binder, in which fiberscomposing the web as the principal ingredient are so less densified toeach other and do not have much contact amongst themselves or with thefiber binder, is subjected to wet and heat conditions at a dryer part soas to melt the fiber binder, the fiber binder shrinks by itself oradheres only to a slight degree to the principal tfibGI'S or among themand forms insignificant intertvvists. Consequently, utilizing efficiencyof the fiber binder is cut down and possibility of an expected strengthwould not be gained, whatsoever.

After due consideration of the above, we inventors first gave attentionto the fact, in a mechanical papermaking process from hydrophobic fiberstock, that it is necessary to make the web retain enough moisture,before the wet web is led to a dryer part, for increasing the efficiencyof the hot water soluble fiber binder. And, we have obtainedsatisfactory results in producing a synthetic fiber paper or sheethaving excellent mechanical properties in dry conditions from syntheticfiber having a moisture regain of not more than 5% by using watersoluble viscous material having good moisture retainability togetherwith the above hot water soluble fiber binder.

Secondly, after prosecuting further studies as to variousafter-treatments, especially heat treatment utilizing thermalcharacteristics of synthetic fiber paper thus formed, We achievedsuccess in producing a fabric-like paper which has characteristicproperties we could hardly expect from the paper just made, andmoreover, in order to make the best use of the effect of the heattreatment, we have established a new method for producing the paper,which comprises, first, forming a sheet paper from a mixed aqueousdispersion of the above hydrophobic fiber with a fiber or fiber-likematerial made from thermoplastic resin having a lower melting point thanthat of the hydrophobic fiber by using a hot water soluble fiber binderand thereafter, subjecting the sheet paper to heat treatment.

Further, we also have scored a success in the provision of anothersynthetic fiber paper having superior physical properties, in which anetwork structure was laminated together with the above synthetic fiberpapers.

Therefore, it is a main object of the present invention to provide animproved process of making a synthetic fiber paper having especiallyexcellent mechanical properties.

It is another main object of the present invention to provide animproved process of making a synthetic fiber paper having variousprominent appearances or shapes and excellent physical properties.

The present invention provides a process of making a sheet papercomprising preparing an aqueous dispersion containing synthetic fiberhaving a moisture regain of not more than 5%, a hot water soluble fiberbinder and carboxymethyl cellulose, and subsequently, forming a sheetpaper from said aqueous dispersion. The term moisture regain is definedas the amount of moisture in a synthetic fiber under prescribedconditions expressed as a percentage of the weight of the moisture-freespecimen (see 118 LO208-1108 and ASTM D 123-68a). The moisture regainvalue is thus a measure of the hydrophobic property of synthetic fibers.The term is herein used to indicate the moisture regain value determinedunder a moisture equilibrium condition at a relative humidity of 95% anda temperature of 20 C.

According to the present invention, as the wet web containing so muchmoisture, in which bonds or intertwists among the fibers composing a wetweb are raised and which is more densified, is moved to a dryer part,utilizing efiiciency of a hot water soluble fiber binder added into thewet web, is raised, and consequently, hydrophobic synthetic fiber paperhaving especially excellent mechanical properties in dry conditions maybe obtained.

As a water soluble viscous material, water soluble natural high polymersuch as gelatin, casein, sodium alginate, etc.; water solublesemi-synthetic high polymer such as starch phosphate, cyanoethylatedstarch, carboxymethyl cellulose, hydroxypropylmethyl cellulose; watersoluble synthetic high polymer such as polyvinyl alcohol, poly-sodiumacrylate, polyacrylamide; and polyethylene oxide, polyphosphate, etc.,which recently have been used as viscous materials for making rayonpaper, vinylon paper, etc., as a substitute for natural hibiscus arelisted. However, from repeated tests for paper making concerning theabove-listed adhesive materials, it was found, as shown in the examples,that the effect of carboxymethyl cellulose was much higher than that ofany other adhesive material, and if other adhesive material was used toachieve the same effect as that of carboxymethyl cellulose, a higherconcentration was needed, and that particularly, polyethylene oxide,polyphosphate, etc. failed to bring about the desired effect becausethey readily formed a film having an adverse effect on a sheetformation.

However, if necessary, use of polyethylene oxide or polyphosphate incombination with carboxymethyl cellulose is allowable. Further, if anonionic surface active agent having a low foaming action is usedtogether with these materials in order to increase the affinity betweenthese hydrophilic viscous materials and hydrophobic synthetic fibers,the above effect is even more raised.

A method for adding carboxymethyl cellulose of the present inventionshould be properly selected so as to be adapted for a paper-makingmachine, thickness of paper, paper-making speed, etc. A superfluousaddition of the material results in many drawbacks, for example, scummedmaterial, too much moisture content of the wet web, inactivedehydration, pollution of felt, etc. So, there is a limit to theaddition amounts of the material. carboxymethyl cellulose having aviscosity from 20 to 5000 centipoise (cps.), preferably from 200 to 2000cps. (measured by B type viscosimeter) in 2% aqueous solution at 25 C.,is used in amounts from 0.003 to 0.1% based on the weight of the aqueousdispersion of fiber.

Carboxymethyl cellulose (hereinafter referred to as CMC for short) isone of the derivatives of cellulose ether formally called sodiumcellulose glycolate having a 4 following structural formula and isutilized for various purposes due to its moisture retainability andprotective colloidal property.

CH OCH COONa H 4|;- 0

The above formula indicates CMC only having a degree of etherificationof 1, that is, one carboxymethyl group per an anhydrous glucose unit.But, theoretically, a degree of etherification may take a numericalvalue not more than 3. In the above formula, n represents a degree ofpolymerization, both which and degree of etherification define thecharacteristics of CMC. Particularly, flow characteristics of an aqueoussolution of CMC largely depend on both the degree of polymerization andthe degree of etherification, for example, CMC of a certain grade hassuch a relation to them as shown in FIG. 1.

FIG. 2 shows a relation between a degree of etherification and abreaking strength of sheet paper, in which viscosities of CMC (cps.) aremeasured in 1% aqueous solution at 25 C. by using B type viscosimeter.As shown in FIG. 2, breaking strength of sheet paper is nearly in aninverse proportion to a degree of etherification in case the viscosityis constant and the breaking strength remarkably increases at the degreeof etherification below 0.6. On the other hand, as shown in FIG. 1 areduction of the degree of etherification exercises an undesirableeffect on water solubility and stability of solution. And, in thepresent invention, from a view of water retainability, it is preferablethat the aqueous solution of CMC has a flow characteristic correspondingto thixotropic gell or the like. From the above reasons, the degree ofetherification should be more than 0.3, preferably from 0.4 to 0.6. Asto a degree of polymerization from a consideration of the relation withflow characteristics of an aqueous solution as shown in FIG. 1 it ispreferably less than 1000, more preferably from 200 to 700. Moreover,CMC may contain salts or moisture to some extent.

It is known that CMC has been utilized in a process of making paper, forexample, nylon paper. However, it was merely utilized as a primarybinder in order to make use of its adherent property, which differsentirely from an object for utilizing CMC according to the presentinvention. On the contrary, the present invention makes a great featureof utilizing CMC together with a hot water soluble fiber binder, that isbased on the fact that, in case CMC is added alone to a hydrophobicfiber such as polyolefine and polyester fiber, it cannot achieve anyeffect as a binder, but, in case of using both the two together, asynergistic effect can be gained.

Hot water soluble fiber binder, referred to as in the present invention,such as polyvinyl alcohol fiber, polyethylene oxide fiber, etc. ispreferably modified so as to melt at a wet-heat condition from 30 C. toC., for example, in the case of a polyvinyl alcohol fiber by adjusting adegree of formalization, and in the case of polyethylene oxide fiber byblending water insoluble substance. When the fiber binder does not meltin a wet-heat condition below 100 C., it also does not melt in an actualsheet forming process. On the contrary, in case the fiber melts in awet-heat condition below 30 C., there is the possibility that it meltsin a process of preparing the dispersion of paper stock. In both cases,an expected fiber binder effect cannot be obtained.

These fiber binders have a fineness from 1 to 15 denier, preferably, notmore than 5 denier and a cut length of less than 20 mm., preferably from3 to 10 mm. If necessary, besides the fiber binder and CMC, addition ofother adhesives, sizing agents, defoaming agents, binders, releasingagents, etc. into a fiber dispersion or a sheet forming bath isallowable.

It goes without saying that the process of the present invention may beapplied to not only polyolefine fiber, polyester fiber, but also otherchemical and synthetic fibers. The latter fibers are also processed inthe same manner as the former using a hot water soluble fiber bindersuch as polyvinyl alcohol fiber. Moreover, the hot water soluble fiberbinder may be previously subjected to a treatment so that the fiberbinder is made insoluble by heat treatment subsequent to theabove-described process.

Further, the present invention provides a process of after-treating asheet paper, which makes it a great feature that the sheet paper, formedby the above-described process, or a sheet paper, formed from an aqueousdispersion containing synthetic fiber having a moisture regain of notmore than a fibrous material having a lower melting point than that ofthe former fiber, a hot water soluble fiber binder, and CMC is subjectedto heat treatment at a temperature below the melting point of the formerfiber.

More particularly, the above process comprises, first, forming a sheetpaper from an aqueous dispersion containing synthetic fiber having amoisture regain of not more than 5% and a fibrous material having alower melting point than that of the former fiber, which melts by beingsubjected to heat treatment subsequent to sheet forming process andachieves an adhesive efli'ect. The fibrous material is made of varioussynthetic resins having a lower melting point than that of polypropylenefiber or polyester fiber, for example, polyethylene, chlorinatedpolypropylene, chlorinated polyethylene, chlorosulphonated polyethylene,ethylene/vinyl acetate copolymer, etc. for polypropylene fiber, andpolypropylene, chlorinated polypropylene, polyethylene, chlorinatedpolyethylene, chlorosulphonated polyethylene, ethylene/vinyl acetatecopolymer, etc. for polyester fiber.

The above process further comprises subjecting the sheet paper thusformed, to heat treatment at a temperature range of above a meltingpoint of the fibrous material and below a shrinking temperature of theformer fiber having a moisture regain of not more than 5%. Through theabove heat treatment, the fibrous material melts and intertwistsphysically and chemically with the principal fibers, which result ingood adhesive effect among the principal fibers.

The fibrous material in the present invention involves (1) so-calledfiber made by a conventional spinning process such as a melt, dry, orrwet spinning process, and fiber-like material, for example (2) fibrousfibril or split piece made from synthetic split film by heating thesame, (3) fibrous structure having an average fineness of not more than2 denier and a cut length of not more than mm. and having a ruggedsurface with many fluffs made from synthetic foam material by applyingshearing force to the foam material, and (4) composite fiber composed oftwo or more kinds of synthetic fibers in which at least one kind ofsynthetic fiber has a lower melting point than that of polypropylene orpolyester fiber, and composite fiber-like structural material.

Up to now, bonding of fibers in a non-woven fabric has been achievedchiefly by applying an adhesive solution or dispersion, or mechanicalpunching or stitching. However, a thin sheet having a hard hand-feelingor appearance and good homogeneity could not be obtained. On thecontrary, in the present invention, the use of fibrous material as atemperature sensitive binder has given such success that the utilizingefiiciency of binder was raised to approximately 100%, and consequently,thin sheets having a good hand-feeling and homogeneity were obtainable.Moreover, according to the present invention, various fibrous binders,for example, broken chips of foam material, split pieces of film, etc.may be utilized besides conventional fiber.

Further, another process of after-treating a sheet paper comprisessubjecting the sheet paper composed of a. synthetic fiber having amoisture regain of not more than 5% or composed of both synthetic fibershaving a moisture regain of not more than 5% and a fibrous materialhaving a lower melting point than that of the synthetic fiber to heattreatment at a higher temeprature, that is, a temperature range from ashrinking temperature of at least 5 C. below a melting point of thesynthetic fiber without applying any substantial tension (or applyingslight tension) for a short time. Through the above process, a finelycreped nonwoven fabric having softness, excellent strength and goodhomogeneity can be produced.

The above process is effective for the non-woven fabric by a dryprocess. But, especially on the synthetic fiber sheet of the presentinvention, that is, the synthetic fiber non-woven by a wet process, ithas a marked effect; good softness, which we could hardly expect fromthe so-called paper-like hand-feeling quite peculiar to the conventionalWet process, is obtainable.

Of course, the shrinking behaviour of fiber depends upon its material,but, even among the same materials, it also largely depends uponmolecular orientation, which is surmised from the amount of tensionapplied to the fiber in a process of manufacture, and upon conditions ofannealing. For example, vinyon fiber, not yet heat treated, shrinks toamounts of 25% under a dry heat condition of 120 C. But, in contrast tothe above, vinyon fiber, already subjected to annealing at C. for 6hrs., shrinks only 2.2% under the same condition.

Therefore, by selecting the condition of treatment in the process ofmanufacture, the synthetic fiber used in the present invention, may haveany shrinkage by the heat treatment of the invention, and so, anydesirable effect could be expected. However, the shrinkage of fiber isusually proportionate to a temperature of the shrinking treatment ,(heattreatment). The higher the temperature, the more the shrinkage. But, incase the thermoplastic synthetic fiber is treated at a highertemperature range in which the fiber melts or intensely softens orshrinks, the fibers feeling is rather hardened after the treatment. Fromthe above reason, the heat treatment of the above process is preferablycarried out at a temperature range from a shrinking temperature to atemperature of at least 5 C. below a melting point or an intenselymelt-shrinking temperature.

The above heat treatment is intended as the wet nonwoven fabric softensdue to its shrinkage. But, it is also noticeable that the shrinkagedepends on the construction of the fabric.

On the other hand, in synthetic fiber paper or wet nonwoven fabric,which contains so much paste or binder having no thermoplastic propertyor having a softening temperature higher than a melting point of theprincipal fiber, shrinkage is considerably limited. So, in case thesheet paper is printed with a paste pattern having little or nosubstantial thermoplastic properties, and thereafter, subjected to theheat treatment, a three-dimensionalpaper with a remarkably raisedpattern may be obtained.

Prior to the above shrinking treatment, a synthetic fiber paper may besubjected to a heat treatment at a temperature below the shrinkingtemperature by a hot air heater or infrared heater, or to a heattreatment at a temperature below the melting point under tension or bycalendering.

Through the above-shrinking treatment, synthetic fiber paper or wetnon-woven fabric loses its surface smoothness and has a bulky and softhand-feeling. Further, as the web density increases due to shrinkage,the bonding of intertwisted fibers and the utilizing efficiency of thebinder, in case the binder is used, is remarkably raised so that theresultant paper or non-woven fabric has excellent mechanical propertiessuch as tensile strength and elongation, bursting strength, tearingstrength, and especially, has a more improved strength in a wetcondition.

Further, the present invention provides a process of making a patternedsheet paper in which a network structure is laminated together with adispersion of fiber into a sheet paper. More particularly, a networkstructure such as an unfolded synthetic split film is stuck on a wet webjust formed from a dispersion of fiber, or, at the same time of the wetweb forming, laminated together with the dispersion of fiber into asheet paper.

Up to now, in order to produce a reinforced paper, a yarn networkstructure such as Victoria lawn has been stuck on or laminated togetherwith the dispersion of fibrous material. In preparation of the yarnnetwork structure, however, a weaving process and a warping process areneeded and further, if colouring is needed, complicated processes suchas dyeing and finishing are added, so the cost is inevitably raised. Onthe contrary, in the synthetic split film of the present invention, thecost may be cut, and a more varied pattern is obtainable.

Moreover, as the split film has a surface with so many fluffs, which, incase the film is laminated with a wet web, intertwist with the web andis united by drying, peeling off between the web layers cannot becreated. In case the split film having a lower melting point than thatof the principal synthetic fiber is laminated together with thesynthetic fiber into a sheet, and thereafter, the sheet is subjected topressing or calendering at a temperature above a melting point of thefilm, patterned paper having a graceful look and a still higher tenacityis obtained. The effect may be achieved in the synthetic fiber paperhaving a large transparency and less density. The larger fineness thesynthetic fiber has and the less the density is, the more prominent itis. In the case of cellulose pulp paper, which is more densified, itwould not be expected.

Synthetic fiber having a moisture regain of not more than as referred toin the present invention, that is, polyester fiber and polyolefinefiber, means fiber of the polymer in which the principal constituentunit is polyester and polyolefine, respectively. In the case ofpolyester, it may be a copolymer of two or more components, and in thecase of polyolefine, it may be a homopolymer of ethylene, propylene,styrene, etc., or a copolymer of two or more components. These polymersmay contain additives such as a stabilizer, antistatic agent, colorant,perfume, etc. A most effective synthetic fiber in accordance with thepresent invention, is polypropylene fiber, which is hydrophobic inexcess and has the least water retainability.

As to the formation of the synthetic fiber, any section, shape ofsurface and crimp does not constitute an obstacle. But, from a viewpointof paper-making ability in using the conventional paper-making machine,the fiber usually has a fineness from 1 to 30' denier, preferably notmore than denier and a cut length not more than 35 mm., preferably from4 to 15 mm. The synthetic fiber may not only be polyester fiber orpolyolefine fiber alone, but also, if necessary, blended with othersynthetic or natural fiber. In the case of blending, blends composed ofsynthetic fibers and composed of more than 60% by weight of syntheticfiber and natural fiber, are most effective. But, the above-syntheticfiber sometimes means the blend of a principal synthetic fiber and asynthetic fibrous material.

As to a machine for executing a heat treatment at a higher temperature,that is, shrinking treatment, any machine, for example, a pin tenter,clip tenter, roller setter, infrared dryer or hot air heater such as asuction drum dryer may be used, but of the types in which width andfeeding speed may be adjusted with ease, are preferable. The suctiondrum dryer type in which the Width and feeding speed are alwaysrestricted, is not preferable.

A synthetic fiber sheet paper thus obtained, a fabriclike sheet obtainedby after-treating the sheet paper and a patterned sheet paper haveexcellent mechanical properties due to a high utilizing effect of thefiber binder, and superior chemical properties such as hydrophobicproperty, insulating property, chemical resistance, due to its ownnature. A sheet paper except a patterned sheet paper, has a lowerdensity, soft hand-feeling and good gas transmission. From the abovefeatures, these sheet papers have various uses, for example, medicalsupplies, filters, padding cloths, insulation tape, surface mats forreinforced plastic, protecting paper for dyeing, packing paper,heatsealing paper, base paper for coating, interlining cloth forsynthetic leather and other materials.

The following examples illustrate specific embodiments of the presentinvention.

Characteristics of paper were measured in accordance with JapaneseIndustrial Standards. Viscosities of an aqueous solution of CMC andother viscous materials were measured by a B type viscosimeter.

All parts and percent are by weight.

EXAMPLE 1 100 parts of polypropylene fiber having a fineness of 1.5 d.and a cut length of 5 mm. and 20 parts of polyvinyl alcohol (hereinafterreferred to as PVA for short) fiber binder (trademark Fibribond No. 241;1.5 d., 5 mm.) were dispersed in an aqueous solution containing 0.01%nonionic surface active agent (trademark Emulgen 905, HLB:9.2). To thisaqueous dispersion, an aqueous solution of CMC having a viscosity from150 to 250 cps. in 1% aqueous solution at 25 C. and a degree ofetherification of 0.54% was added to prepare an aqueous dispersioncontaining 0.006% CMC. A hand sheet of polypropylene fiber was made fromthe dispersion by a Tappi standard method and the sheet was adhered to aphotographic ferrotype plate and subjected to infrared drying at asurface temperature of 110 C.

Strength of the paper is shown in Table 1 column (A) in comparison withthose of various papers which were made in the same manner as the aboveexcept (B) using CMC without the PVA fiber binder, (C) using 20% of PVAfiber binder without CMC, (D) not using either binder now CMC (B) using20% of PVA fiber binder and sodium alginate as a substitute for CMC (F)using 20% of PVA fiber binder and polyethylene oxide as a substitute forCMC. The polyethylene oxide having a viscosity of 500 cps. in 1% aqueoussolution was used at a concentration of 0.02% based on the weight of theaqueous dispersion of the fiber.

1 Viscosity of 200 cps. (viscosimeter type B) in 1% aqueous solution.Viscosity of 370 cps. in the same.

A paper-making machine, as referred to in the present invention, may beof a conventional type such as Fourdrinier machine, Short wire papermachine, cylinder machine and of a new type such as Rotoformer,Vertiformer,

etc.

From the table it will clearly be understood that, in both cases of (C)not using CMC in the least, admitting that the web contains 20% of PVAfiber binder and (F) using polyethylene oxide as 'viscous material,strength of the paper could hardly be gained, and, in case (B) of usingsodium alginate, which being less sticky in itself as viscous material,little effect of increasing the strength is gained, also. n thecontrary, when PVA fiber binder and CMC are used together (A), theeffect of the PVA fiber binder is remarkably enhanced and the strengthis exceptionally increased.

EXAMPLE 2 100 parts of polypropylene fiber having a fineness of 1.5 d.and a cut length of 5 mm. and 20 parts of PVA fiber binder weredispersed in an aqueous solution containing a 0.01% nonionic surfaceactive agent. To this dispersion, (G) an aqueous solution of CMC havinga viscosity from 300 to 350 cps., in 1% aqueous solution at 25 C. anddegree of etherification from 0.6 to 0.67 and (H) aqueous solution ofCMC having a viscosity from 500 to 1000 cps. and a degree ofetherification from 0.55 to 0.57 were added separately to prepare twokinds of aqueous dispersions, both containing 0.006% CMC. Hand sheets ofpolypropylene fiber were made in the same manner as in Example 1.Strength of the papers is shown in Table 2.

1 0 EXAMPLE 4 75 parts of polypropylene fiber having a fineness of 1.5denier and a cut length of 5 mm., 15 parts of polyethylene fiber havinga fineness of 6 denier and a cut length of 5 mm., and 15 parts of PVAfiber binder (trademark Fibribond No. 24l) having a fineness of 1 denierand a cut length of 4 mm. were dispersed with a nonionic surface activeagent to prepare an aqueous dispersion containing 2% fibers. To thedispersion, an aqueous solution of CMC having a viscosity from 150 to250 cps. in 1% aqueous solution at 25 C. and a degree of etherificationof 0.65% was added to prepare an aqueous dis persion containing 0.01%CMC, and further, small quantities of a sizing agent and defoamingagent, respectively, were added. The dispersion was put into a papermaking bath and the concentration of CMC was adjusted to 0.006%. Fromthe bath, paper was made at a speed of 160 m./ min. by using a cylinderpaper machine.

A surface temperature of the Yankee drier of the machine wasapproximately 100 C.

The paper, thus obtained, had a soft hand feeling like non-woven fabircand excellent mechanical properties. The paper was subjected to heattreatment at 125 C. for 4 min. so that the polyethylene fiber wasmelted.

Thusly obtained polypropylene fiber paper was remarkably increased inits strength andrhad little difference of strength between dry and wetconditions. Mechanical properties of the papers are given in Table 4.

From a result of the above and Example 1, it will be proven that thelower the degree of etherification of CMC, and the higher the viscosity,that is, the higher the degree of polymerization, the more CMC enhancesthe effect of increasing strength of the paper.

EXAMPLE 3 100 parts of polyester fiber having a fineness of 2.0 denierand a cut length of 5 mm. and 20 parts of PVA fiber binder weredispersed into an aqueous solution containing 0.01% nonionic activeagent. To this aqueous dispersion, an aqueous solution of CMC having aviscosity from 150 to 250 cps. in 1% aqueous solution at 25 C. and adegree of etherification of 0.54% was added to prepare an aqueousdispersion containing 0.006% CMC. A hand sheet of polyester fiber wasmade from the dispersion in the same manner as in Example -1 and thesheet was adhered to a photographic ferrotype plate and subjected toinfrared drying at a surface temperature of 110 C.

Strength of the paper was shown at Table 3 column (A) in comparison withpaper (B) which was made in the same manner as the above except foradding only PVA fiber binder without CMC.

The paper had strong hydrophobic and oleophilic properties and goodinsulating resistance due to the specific characteristics of theoriginal polypropylene fibrous material and displayed excellentdimensional stability.

Further, in a process of web forming from the dispersion of fiber in theabove Example 4, a spread split film made from coloured polypropylenefilm was laminated together with dispersed fiber into a paper layer. Theresultant paper had a graceful looking-coloured network which could beseen through the paper layer and had a still higher tenacity.

On the other hand, to the aqueous dispersion of fibrous material in theabove Example 4, as a substitute for CMC, an aqueous solution ofpolyethylene oxide having a viscosity of 500 cps. in 1% aqueous solutionat 20 C. was added to prepare an aqueous dispersion containing 0.03%polyethylene oxide, and further, small quantities of a sizing agent anddefoaming agent were added, respectively, to the dispersion. From a'bath filled with the dispersion, paper was made at a speed of 160m./min. by using a cylinder paper machine. A surface temperature of theYankee dryer of the machine was approximately C. Web-like loosestructure of polypropylene could barely be formed from the dryer, whichhad not enough strength to maintain a sheet-like shape.

EXAMPLE 5 Polyethylene foam sheet (made from low-density polyethylene)having a bulk density of 0.03 g./cm. and a thickness of 10 mm. in whichindividual foam was basically independent but partially connected atportions to each other, was cut into chips of approximately 60 mm? by acutter. 20 g. of the chips were put into a mixer (NATIONAL MX-120;number of revolutions, 1800 r.p.m.) together with 2 litres of water and0.2 g. of a nonionic surface active agent (trademark Emulgen 905,HLB=9.2) and stirred violently for 30 min. From the stirring, the chipswere broken into pieces having a shape similar to wood pulp. Thestirring was repeated 4 times. Broken chips, thus obtained, were putinto a Niagara test beating machine (capacity, 10 litres; number ofrevolutions 450 rpm.) together with 1 g. of nonionic surface activeagent (Emulgen 905), and, in a concentration of 80 g./ litre, subjectedto beating for 30 min. under an unbound condition. Thus, polyethylenefibril was obtained from the foam sheet.

From an examination of the polyethylene fibril by a microscope, thefibril was found to be a piece having a slender shape with manyfibrillated fiuifs. All the pieces had a length of less than 10 mm. anda fineness of less than 2 denier.

On the other hand, 2 g. of polypropylene fiber having fineness of 1.5denier and a cut length of 5 mm. and 0.2 g. of PVA fiber binder(trademark Fibribond No. 243) were put into a water bath (2 litres)together with 0.2 g. of nonionic surface active agent (trademark Emulgen905, HLB=9.2), and stirred to prepare a uniform dispersion of fibers.

To the dispersion, 0.5 g. of the above polyethylene fibril was added.After uniform mixture and dispersion were realized by further stirring,an aqueous solution of 0.2 g. CMC having a viscosity from 150 to 200cps. in 1% aqueous solution and a degree of etherification of 0.54% as aviscous material was added. A hand paper of polypropylene fiber was madefrom the dispersion by the Tappi standard method. The paper, thusobtained, was dried under a predetermined condition, and then, subjected to heat treatment in a hot air dryer at a temperature of 130 C.

Mechanical properties of the paper are shown in Table 5, in comparisonwith those made in the same way as the above except not adding thepolyethylene fibril.

EXAMPLE 6 A foam sheet having a bulk density of 0.51 g./cm. and athickness of 3.0 mm. in which individual foam was basically independentbut partially connected at portions to each other, was made by using ablowing agent from ethylene/vinyl acetate copolymer containing 28% vinylacetate (trademark Evafiex 260, made by Mitsui Polychemical Go) From thesheet, ethylene/vinyl acetate copolymer fibril was prepared in the samemanner as Example 5. A formation of the fibril was confirmed by amicroscope.

n the other hand, 2 litres of the same dispersion of polypropylene fiberand PVA binder fiber as that in Example was prepared. 0.5 g. of theabove ethylene/ vinyl acetate copolymer fibril was added to thedispersion and after a uniform mixture and dispersion were realized bystirring, an aqueous solution of the same CMC as in Example 5 was addedas a viscous material. A hand-made paper of polypropylene fiber was madefrom the dispersion by the Tappi standard method. The paper, thusobtained, was dried under a predetermined condition, and then, subjectedto heat treatment in a hot air dryer at C. for 10 min.

The resultant paper had a basis weight of 50 g./m. dry-breaking strengthof 3.2 kms., wet-breaking strength of 2.1 km., dry elongation of 5.6%,and tear factor of 5100.

A ratio of ethylene/vinyl acetate in the copolymer of the presentinvention may be varied in compliance with an adhesion to the fibercomposing the principal ingredient of paper and other requirements.However, it is preferable that the copolymer contains from 15 to 45% byweight of vinyl acetate, and, in case a content of vinyl acetate in thecopolymer exceeds 45 by weight, a melting point of the resultantcopolymer drops below 60 C. and a blocking resistance is reduced, thatis, the copolymer loses its function as a binder.

EXAMPLE 7 Polyethylene foam sheet (low-density polyethylene) having abulk density of 0.03 g./cm. and a thickness of 7 mm. in which individualfoam was basically independent but partially connected at portions toeach other, was cut into chips of approximately 50 mm. by a cutter. 200g. of the chips were put into a mixer (mono phase four pole motor,number of revolutions 2000 1'.p.m.) which was provided with rotatingblades of thickness 5 mm. and of a pointed head 1 mm. and which had acapacity of 30 litres, together with 2 litres of water and 2 g. ofnonionic surface active agent (trademark Emulgen 905) and stirredviolently for 30 min. By the stirring, the chips were broken into pieceshaving a shape similar to wood pulp. Broken chips, thus obtained, weresubjected to heating by using a Hollender beater (capacity of 3000litres, roll diameter of 1250 mm., roll blade thickness of 7 mm., numberof blades 84, prop-up blade thickness 4 mm.) at a concentration of 1%under an unbound condition for 60 min. From an examination by amicroscope, the polyethylene fibril, thus obtained, was found to be apiece having a slender shape with many fibrillated fiuffs. The piecealso had a length of less than 10 mm. and a fineness of less than 2denier.

On the other hand, polypropylene fiber having a fineness of 1.5 denierand a cut length of 5 mm., 20% of the above polyethylene fibril and 15%of PVA fiber binder both based on the weight of polypropylene fiber wereput into a chest (capacity 5000 litres) at a concentration of 2%, andthen predetermined amounts of a nonionic surface active agent as adispersing agent and CMC having a degree of etherification of 0.65 as aviscous material were added. Paper was made from the dispersion by acylinder machine. The paper had a basis weight of 32 g./m. uniformdispersion of fibers, good quality and soft feeling.

Further, the paper was subjected to heat treatment using a heat calender(temperature of roll surface, C.; roll pressure, 5 kg./cm. (gage press))or using a tenter (at C., for 4 min.), which resulted in the paperhaving excellent strength and a slight difference between dryandwet-tenacity. The mechanical properties are shown in Table 6.

All the fibrils used in the above Examples 5, 6 and 7 usually appear asfibrous structures having a rugged and flufied surface, although theymay be of various forms to some degree chiefly depending on a foamstructure of sheet material. In view of its efiiciency as a binder, thefibril has an average denier preferably less than 2 and a cut lengthless than 10 mm. As the fibril has so few vesicles in its innerstructure, if any, it scarcely displays elasticity and its bulk specificgravity nearly equals that of the polymeric material itself composingthe foam material.

EXAMPLE 8 Polypropylene fiber having a fineness of 1.5 denier and a cutlength of 5 mm., of polyethylene fiber fibril and 10% conventional PVAfiber binder (trademark Fibribond No. 243), both based on the weight ofthe of conventional PVA fiber binder (Fibribond No. 243) were put into apoacher at a fiber concentration of 1% together with predeterminedamounts of a nonionic surface active agent as a dispersing agent and CMC(trademark Cellogen WSC made by Daiichi Kogyo Seiyaku Co.) having adegree of etherification from 0.6 to 0.7 and a viscosity from 150 to 250cps. at 1% aqueous solution as viscous material, respectively. Paper wasmade from the dispersion by a cylinder machine. The paper had a basisweight of 35 g./m. and displayed a uniform dispersion of fibers goodquality and soft feeding.

Further, the paper was subjected to heat treatment at 140 C. for 1 min.by using a roller setter without giving any tension to the widthdirection. The paper thus obtained, had remarkably improved physicalproperties and a feeling and appearance like fabrics. The properties areshown in Table 8.

polypropylene fiber, were put into a chest, and then, predeterminedamounts of a nonionic surface active agent (HLB=9.2) as a dispersingagent and CMC having a degree of etherification of 0.65 were added.Paper was made from the dispersion by a conventional cylinder machine.The paper had a basis weight of g./m. and displayed uniform dispersionof fibers, good quality and soft feeling.

Further, the paper was subjected to heat treatment using an infraredheater at 140 C. Tenacity and elonga- A composite rfiber as is referredto in the present invention, is not limited to the one in the aboveexample which was a side-by-side type and had a composite ratio of 1:1.A composite ratio may be varied from a viewpoint ofcomposite-spinnability, that is, a content of polymer having a lowermelting point may decrease according to a proportional ratio. In theabove case, however, the content cannot decrease so much that thepolymer having a lower melting point has a composite ratio of less than20% by weight based on the whole web sheet. Also, a

tion of the paper thus obtained, were as shown in Table 7. section ofcomposite fiber may be of various forms, for

The above measurements were made on a test piece of 1.5 cm. (width) x 20cm. (length) in accordance with Japanese Industrial Standards.

Polyethylene fibril, which may be used in the present invention, isprepared as follows: low density or mediumor high-density polyethylenefilm (high density polyethylene film of 20,11. thickness was used in theabove Example 8) are split into tapes as thinly as possible, preferablyin a thickness from 10 to loop, by a conventional method, and the splittape is cut into chips of lengths from 1 to 15 mm., preferably from 3 to10 mm. by a cutter, and then subjected to beating under predeterminedconditions using a beater usually used in paper making from pulp, andthusly, transformed into small fibrous chips of an average fineness from0.1 to 10 denier, preferably 2 denier.

EXAMPLE 9 Polypropylene fibers of a fineness of 1.5 denier and a cutlength of 5 mm., 40% based on the weight of polypropylene fiber, of aside-by-side type composite fiber having a fineness of 3 denier and acut length of 6 mm., which was composed of polypropylene (PP #2000, madeby Mitsubishi Petroleum Chemical Co.) and polyethylene (DNDJ-0405, madeby Nitto Unikar Co.) at a ratio of 1:1, and 10% based on the weight ofboth above fibers,

example, side-by-side type, sheath-core type such as concentric-circulartype, random type, etc. Particularly, a concentric-circular typecomposite fiber, in which the polymer of a lower melting point islocated at the outer side in its section, is most preferable.

EXAMPLE 10 Polypropylene fibers (Pylene, made by Mitsubishi Rayon Co.)having a fineness of 1.5 denier and a cut length of 5 mm. and 15% byweight of PVA fiber binder (Fibribond 'No. 423) based on the above fiberwere put into a poacher to prepare a 2% dispersion of fiber togetherwith a nonionic surface active agent (Emulgen 905) as a dispersing agentand CMC having a degree of etherification from 0.6 to 0.7 and aviscosity from 150 to 250 cps. at 1% aqueous solution, the added amountof both were 500 g. and 1 kg, respectively, both based on 5000 kg. ofwater. From the dispersion, a paper having a basis weight of 37 g./m.was made by a cylinder machine.

The polypropylene fiber paper was subjected to a continuous heattreatment without giving any tension in a hot air dryer at 140 C. for 11min. The paper thus obtained, had a basis weight of 'g./m. and a softhandfeeling like dry nonwoven fabric, which were due to 15 shrinkage bythe above heat treatment. The mechanical properties were as shown inTable 9.

1 (i= X W X 0.482 X 10 -C=Drape stiffness; W=Weight in oz./sqyd. ofcloth (according to COG-T4916).

1 Emery paper No. 600 was used.

On the other hand, when the polypropylene fiber paper, not yet subjectedto a continuous heat treatment in the above example, was printed, apattern with paste having no substantial thermoplastic properties, forexample, starch paste, and thereafter, subjected to heat treatment,three-dimensional paper with a remarkably raised pattern was obtained.

EXAMPLE 1.1

80 parts of polypropylene fiber having a fineness of 1.5 denier and acut length of 5 mm., 20 parts of polyethylene fiber having a fineness of6 denier and a cut length of 5 mm., and 20% by weight of PVA fiberbinder (Fibribond No. 243) based on the above two fibers were used asstock for paper-making. The paper, made in the same manner as in Example10 by using a cylinder machine, was directly subjected to, or, afterpreheated by a hot calender (surface temperature 110 (3., roll pressurekg./cm. (gage press)) so that the polyethylene fiber just melted, andthen, subjected to a continuous heat treatment at 155 C. for l min. byusing a pin tenter adjusted at a feed of and a width-directionalshrinkage of Through the heat treatment, the paper shrank to the amountof 25 in the machine direction and 30% in the width direction and lostits paperlike or film-like feeling, that is, the former had a rawpaperlike appearance and the latter had a paper-after-calendering typeappearance, respectively. It had a soft hand-feeling like fabric. Themechanical properties were as shown in Table 10.

and 5% by weight of PVA fiber binder based on the weight of the abovethree fibrous materials were used as stock for paper making. The paper,made in the same manner as in Example 4 by using a cylinder machine, wassubjected to a continuous heat treatment at 155 C. for 1 min. by using apin tenter similar to that of Example 10.

The paper, thus obtained, had a soft and bulky hand feeling, and littledifference in strength between dry and wet conditions. Mechanicalproperties are shown in Table 11.

TABLE 11 Before After shrinking shrinking Basis weight (g./m. 25 40Breaking strength (km.):

Dry:

Machine 2. 10 5. 10 Traverse 1. 58

Machine 0. so a. 20 Traverse. 1. 10 Hand feeling 1 Impossible tomeasure. 2 Paper-like. 3 Soft non-woven fabric-like.-

What we claim is:

1. A process of making a sheet paper comprising preparing an aqueousdispersion containing synthetic fiber having a moisture regain of notmore than 5%, hot water soluble polyvinyl alcohol fiber binder inamounts from 5 to 25% based on the weight of said synthetic fiber andcarboxymethyl cellulose, in amounts from 0.003 to 0.1% based on theweight of said aqueous dispersion and subsequently, forming a sheetpaper from said aqueous dispersion.

2. A process as claimed in claim 1, wherein said carboxymethyl cellulosehas a degree of etherification from 0.4 to 0.6.

3. A process as claimed in claim 1, wherein said synthetic fiber havinga moisture regain of not more than 5% is polyolefine fiber.

4. A process as claimed in claim 1, wherein said synthetic fiber havinga moisture regain of not more than 5% is polyester fiber.

5. A process as claimed in claim 1, wherein a network structure islaminated together with said dispersion of fiber into said sheet paper.

TABLE 10 Preheated sample by Raw sample calender After Before AfterBefore shrinking shrinking shrinking shrinking 1, 750 [2, 10] 1, 190 [2.32] 1, 190 [2. 47] 1, 20412.43] Traverse 335 [0.40] 206 [0.39] 552[0.69] 336 [0.67] Breaking strength (km.) wet:

Machine 1, 120 [L34] 545 [1.00] 1,748 [2.20] 985 [1.98] Traverse 210[0.25] 118 [0.22] 305 [0.46] 205 [0.41] Tearing factor 420 285 510 256Bursting factor 2. 10 1. 83 2. 41. 1. 96 Hardness, G Value Machine 0.750.87 0. 73 0. 90 Traverse 0. 06 0.09 0.05 0. 20 Surface abrasionresistance (times). 2, 100 550 2, 600 1,150

On the other hand, in the case where the raw paper, just made in theabove Example 11 was subjected to heat calendering by using an embossedcalender roll having a surface temperature from 110 C. to 130 C. and alinear pressure of more than 1 kg./cm. (gage press), three-dimensionalembossed paper, which had many dimensionally stable projections and nofluifs, was obtained.

EXAMPLE 12 parts of polypropylene fiber having a fineness of 2 denierand a cut length of 5 mm., 15 parts of polyethylene fiber having afineness of 6 denier and a cut length of 5 mm, 35 parts of beaten pulp(NBKP 35 SR), a melting point of said fibrous material and below a 17shrinking temperature of said fiber having a moisture regain of not morethan 9. A process as claimed in claim 7, wherein said fibrous materialhaving said lower melting point is polyethylene or its derivatives.

10. A process as claimed in claim 7, wherein said fibrous materialhaving said lower melting point is an ethylene/vinyl acetate copolymercontaining from 15 to 45 by weight of vinyl acetate.

11. A process as claimed in claim 7, wherein said fibrous materialhaving said lower melting point is a fibrous fibril made from syntheticsplit film by beating same to be fibrillated.

12. A process as claimed in claim 11, wherein said fibrous fibril ispolyethylene fibril.

'13. A process as claimed in claim 7, wherein said fibrous materialhaving said lower melting point is a fibrous structure having an averagefineness of not more than 2 denier and a cut length of not more than mm.and having a rugged surface with manyl fluffs, which is made fromsynthetic foam material by applying a shearing force to said syntheticfoammaterial.

14. A process as claimed in claim 7, wherein said fibrous materialhaving said lower melting point is a short length staple having afineness of not more than denier, which being made by a melt-spinningprocess.

15. A process as claimed in claim 7, wherein said aqueous dispersioncontains polypropylene fiber as said fiber having a moisture regain ofnot more than 5% and from 10 to 35% by weight of polyethylene fiber assaid fibrous material having a lower melting point based on a weight ofsaid former fiber.

16. A process as claimed in claim 15, wherein said sheet paper, whichbeing formed from said aqueous dispersion, is subjected to printing of athree-dimensional pattern by applying heat and pressure.

17. A process as claimed in claim 7, wherein said aqueous dispersioncontains polypropylene fiber as said fiber having a moisture regain ofnot more than 5% and from to 50%, based on a weight of said former fiberof a short length staple of a composite fiber composed of polypropyleneand polyethylene having a fineness of not more than 15 denier as saidfibrous material having a lower melting point.

18. A process as claimed in claim 1, wherein said sheet paper issubjected to heat treatment at a temperature range from a shrinkingtemperature to a temperature of at least 5 C. below a melting point ofsaid fiber having said moisture regain of not more than 5% withoutapplying any substantial tension.

19. A process as claimed in claim 7, wherein said sheet paper havingbeen formed from said aqueous dispersion is subjected to heat treatmentat a temperature range from a shrinking temperature to a temperature ofat least 5 C. below a melting point of said fiber having said moistureregain of not more than 5% without applying any substantial tension.

20. A process as claimed in claim 7 wherein said fibrous material havingsaid lower melting point is used in amounts from 5 to based on a weightof said synthetic fiber having a moisture regain of not more than 5%.

21. A process as claimed in claim 18, wherein said sheet paper isprinted with a paste pattern, said paste having little or no substantialthermoplastic properties and thereafter, subjected to heat treatment.

22. A process of making paper comprising preparing an aqueous dispersioncontaining principal fiber selected from the group consisting ofpolypropylene and polyester with the addition of 5% to 25 by weight ofpolyvinyl alcohol fiber and an aqueous solution of carb0xymethylcellulose in an amount from 0.003 to 0.1% based on the weight of theaqueous dispersion of fiber, and subsequently forming a sheet of paperfrom said aqueous dispersion.

23. A process according to claim 22, further comprising briefiy heatingsaid sheet of paper to a temperature of the order of C. to C.

24. A process according to claim 22, in which the principal fiber usedis polypropylene, further comprising the steps of treating foam of acomposition selected from the group consisting of polyethylene andethylene/vinyl copolymer to convert said composition to fibril form andincluding said fibril in said dispersion in an amount of approximately20% to 25% by weight of said polypropylene fiber.

References Cited UNITED STATES PATENTS 2,810,644 10/ 1957 Shearer 162177X 3,114,670 12/1963 Iwasaki 162146 3,431,166 3/1969 Mizutani et a1.l62l46 X HOWARD R. CAINE, Primary Examiner Us. 01. X.-R.

